It'll be soon clear that wrenches and I don't get along, but I try to get all the advice I can to compensate. I've had for years a 1980 Volare slant six with the overdrive manual transmission, not driven often. A problem popped up in the very hot summer we had last year that hasn't happened before: after driving a few miles without problem the car would then briefly stumble when put under a load (accelerating in a lower gear or shifting to a higher gear), and the engine would then die, all six cylinders at once.

But downshifting or letting off the throttle would instantly bring the engine back to life, and not by "bumpstarting" the engine either. It would idle fine and rev freely in neutral. It doesn't sound like vapor lock at all. When I drove the car in more moderate summer heat it would act up the same, but take longer to do so, and in winter the problem goes entirely away.

I replaced the ignition coil as the symptoms seemed to be electrical, but to no effect. Internet searches haven't helped because the symptoms seem to be unique. Cold eliminates the problem, warm weather makes it slightly prone to the problem, and really hot weather partly cripples the car. (I can limp it home even at its worst.) The gas gets siphoned and fresh stabilized gas put in yearly, since I don't drive it enough to burn a whole tank. The problem started just last year. Any ideas?

5/8/14: Sorry for the lag, I don't even know how to respond on sites like this. Local advice from the shop that fixes my cars was that it sounded like a fuel problem, probably the gas filter. I changed the filter late last year and the car ran fine in the cold weather, but it tended to anyway in very cold weather (see above). But now in warmer weather it still runs fine. The problem may have merely been a partly clogged filter, of all things.

 

It may be the fuel to much ethanol in the mix is causing a boiling of the fuel.
maybe....
keep the heat away from the fuel lines and the carb.

 

Non-ethanol gas is still available around here and it's all I run. I've seen vapor lock before; my Volare problems don't seem anything like that.

 

Could be a number of thigs , weak coil comes to mind , with more load the spark is too weak to light the plugs , bad plugs could be a problem too

 

I would check all the rubber fuel lines at the tank If they are Ok I would put a fuel pressure gauge on it and go for a drive...

 

I'll have to try the fuel pressure gauge approach just to verify or eliminate that possibility. Unsure why hot weather would affect fuel flow, but who knows?

 

how old is the radiator? It could be your overheating the engine. NOt likely but its a possibility.

Something to check is the heat riser valve on the exhaust. It should turn freely if not lubricate it with some oil. If it is stuck closed in winter the car will run rich and probably fine. In warmer weather the engine will stall.

 

That's not a lean burn is it?
Do not just throw parts at it.
That can get costly and you never really learn what was wrong.

Do you have a working temp gauge on it?
Is the motor itself getting hotter during the hot weather?
Have you done a good tune up lately?
Do you know how to read your spark plugs?

I would have to agree, you have a weak spark. I would think if it was fuel related, it would not start right up when you just let off the throttle or down shift. Unless there is a plugged filter or line and it just can't keep up. Or maybe a sunk float and you don't have enough gas to keep up. I don't see how heat would affect that though. Maybe a rubber hose is close to the exhaust or something and it sucks closed when hot.
Weak spark sounds closer to the problem.
Could be as simple as a cracked or dirty distributor cap.
I would look into that tune up. Plugs, cap, rotor, & wires. Along with fuel, oil, and air filter.
Obviously something is getting hot